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Tuesday November 23, 2010

Tuesday November 23, 2010. You need your notebooks today. We are beginning our chapter on the cell membrane. Turn a sheet of paper sideways. In the center of the sheet, draw a membrane like the one on the board. On the left, make a chart titled: The 4 Roles of a Cell Membrane.

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Tuesday November 23, 2010

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  1. Tuesday November 23, 2010 • You need your notebooks today. • We are beginning our chapter on the cell membrane. • Turn a sheet of paper sideways. • In the center of the sheet, draw a membrane like the one on the board. • On the left, make a chart titled: The 4 Roles of a Cell Membrane. • On the right, make a chart titled: The 4 Membrane Bound Proteins.

  2. Homeostasis • Discovery

  3. Objectives: Cell Transport/Homeostasis Unit • To understand how particles such as water, nutrients, macromolecules and bacteria transport across cell membranes making them semi permeable and be able to evaluate passive and active methods of cell transport.

  4. Objectives Cell Membrane • Understand how the cell membrane helps a cell maintain homeostasis. • Identify the ways the cell membrane restricts the exchange of substances. • Identify 4 membrane proteins. • List the functions of membrane proteins. • Vocabulary • Phospholipid • Lipid Bilayer

  5. Cause & Affect • When it’s cold outside, we shiver. • Why? • When it’s hot outside, what do we do? • We sweat. • Why? • Sweating & shivering are just two examples of our bodies trying to maintain a regular body temperature. • Who remembers what this process is, one of the properties of life, that causes us to maintain balance in a changing environment?

  6. Inside our Bodies • The process of any organism trying to maintain balanced, stable internal conditions in a changing environment is called homeostasis. • It’s natures balancing act it does because the world always changes. • What about inside our bodies? • Does our internal environment change at all? • How? • What about the concept of dehydration? • What do you do to fix this? • How do you know to do this? • Do you not feel thirsty?

  7. Homeostasis • Being thirsty is a chemical solution to satisfying our body’s need for water. • As our water levels change in our bodies we have to adjust these to be as healthy as possible. • This is just one reaction that takes place in our bodies but all living things react to their environments. • These reactions help organisms maintain homeostasis.

  8. Homeostasis, continued • Individual cells, as well as organisms, must maintain homeostasis in order to live too. • One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane. • In our continued study of cells, we are going to focus on how cell’s maintain homeostasis by the properties of the cell membrane.

  9. Cell Membrane • Cells are suspended in a fluid environment. (like in blood) • Even the cell membrane is fluid. It is made up of a “sea” of lipids in which proteins float. • By allowing some materials but not others to enter the cell, the cell membrane acts as a gatekeeper. • The cell membrane also provides structural support to the cytoplasm, recognizes foreign material, and communicates with other cells, all of which contribute to maintaining homeostasis.

  10. The Cell Membrane

  11. Homeostasis What are the four functions that the cell membrane performs to maintain homeostasis? • Regulates what goes in and out of the cell. • Acting as a gate keeper • To provide structural support. • Provides pressure against the internal environment • Recognizes foreign material. • Uses ‘feelers’ called receptors to identify good and bad stuff in the immediate area • Communicates with other cells. • Uses the ‘feelers’ to organize with other cells into tissues

  12. Lipid Bilayer

  13. Lipid Bilayer • The cell membrane is made of phospholipids. • A phospholipid is a specialized lipid made of a phosphate “head” and two fatty acid “tails.” • It is a lipid that contains phosphorus and that is a structural component in cell membranes. • The phosphate head is polar and is attracted to water. • The head is water ‘loving’ = HYDRO - PHILLIC • The fatty acid tails are nonpolar and are repelled by water. • The tail is water ‘hating’ = HYDO - PHOBIC

  14. Visual Concept: Phospholipid

  15. Polar Head Non-Polar Tails WATER REGION Phospholipid • Polar Heads are HYDROPHILLIC • They love water • Made of phosphates • Tails are HYDROPHOBIC • They hate and are afraid of water. • Made of fatty acids NON- WATER REGION

  16. Visual Concept: Cell Membrane Outside of Cell Inside of Cell

  17. Lipid Bilayer, continued Structure • Because there is water inside and outside the cell, the phospholipids will naturally form a double layer called the lipid bilayer. • The basic structure of a biological membrane, composed of two layers of phospholipids • The nonpolar tails, repelled by water, make up the interior of the lipid bilayer. • The polar heads are attracted to the water, so they point toward the surfaces of the lipid bilayer. • One layer of polar heads faces the cytoplasm • The other layer is in contact with the cell’s immediate surroundings outside.

  18. Visual Concept: Lipid Bilayer

  19. Fluid Mosaic Model • The cell membrane isn’t rigid. • It has the ability to be squeezed and move around. • This is called the Fluid Mosaic Model of the membrane.

  20. Lipid Bilayer Barrier • Only certain substances can pass through the lipid bilayer. • The phospholipids form a barrier through which only small, nonpolar substances can pass. • This feature makes the membrane SEMIPERMIABLE, or allowing only desired substances to cross into the cell. • Ions and most polar molecules are repelled by the nonpolar interior of the lipid bilayer and therefore have to be ushered in other ways.

  21. Polar Molecules, like water, are repelled by the polar heads of the phospholipid bilayer. Other non-polar molecules, like carbon dioxide, are not repelled and allowed to flow through the bilayer.

  22. Membrane Proteins • Homeostasis is also helped out by various proteins that can be found in the cell membrane. • Some proteins face inside the cell, and some face outside. Other proteins may stretch across the lipid bilayer and face both inside and outside. • Proteins are made of amino acids. Some amino acids are polar, and others are nonpolar. • The attraction and repulsion of polar and non-polar parts of the protein to water help hold the protein in the membrane.

  23. Membrane proteins What are the 3 major types of membrane proteins? • Receptor proteins: these are the ‘feelers’ that identify good and bad substances in the environment • Transport proteins: allow large and polar substances to pass through the membrane • Tethered & Anchored Proteins: • Enzymes: catalyze reactions that happen on the inside of the cell • Cell surface markers: glycoproteins are proteins with attached sugar chains. These chains of sugars (remember polysaccharides and carbohydrates) act as markers to help identify themselves to other cells

  24. Membrane Proteins

  25. Questions?…

  26. Build a Membrane Activity • Go to your groups and gather your supplies. • For the remainder of the period you will build a cell membrane.

  27. Build a Membrane Directions • Color the parts (neatly) described on the board. • Cut out the phospholipid bilayer (page S2) along the solid lines. Cut all the way to the edges of the paper in the direction of the arrows. • Fold the phospholipid bilayer along the dotted lines and tape the edges together to form a fully enclosed rectangular box. • Cut out each protein (pages S3 and S4) along the solid black lines and fold along the dotted lines. • Form a 3-D shape by joining the protein sides and tops together and tape them in to place. Use the tabs to help you. • Tape the 3-D proteins into place along the edges of the phospholipid bilayer. • By staggering the membrane proteins back and forth along both long sides of the bilayer “box”, the whole model will stand up by itself on a table.

  28. Summary • One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane. • The lipid bilayer is selectively permeable to small, nonpolar substances. • Proteins in the cell membrane include cell-surface markers, receptor proteins, enzymes, and transport proteins.

  29. Group Discussion/Reflection Talk in your groups to answer the following questions. • Identify the 4 functions of the cell membrane that allows it to maintain homeostasis • If I said the cell membrane is like a “gatekeeper” what does that mean? • How does the membrane regulate things going in or out of the cell? What is that property called? • What are the 4 types of proteins within the cell membrane and describe the structure/function of each of them.

  30. Group Discussion/Reflection Talk in your groups to answer the following questions. • Identify the 4 functions of the cell membrane that allows it to maintain homeostasis • If I said the cell membrane is like a “gatekeeper” what does that mean? • How does the membrane regulate things going in or out of the cell? What is that property called? • What are the 4 types of proteins within the cell membrane and describe the structure/function of each of them.

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